1. Field of the Invention
The present invention pertains to a pnuematic timing apparatus comprising a cylinder and piston actuator having differential effective pressure fluid areas on the piston which are in communication with a compressed air circuit including at least one orifice arranged such that a predetermined cycle timing function may be maintained substantially independent of variations in the air pressure in the circuit. The timing actuator is particularly adapted for use in conjunction with a pneumatic cleaning system for impingement type dust collector/filter units, for delivering momentary large volumes or pulses of pressure air for enhancing material flow from bulk material storage bins, and other apparatus utilizing the energy of pressure fluid flow.
2. Background Art
There are several applications for compressed air and other pressure fluids wherein periodic momentary flow of air is desired on a substantially constant cyclic basis. Although various pneumatic and other pressure fluid control systems are known which include timing devices for the periodic commencement or interruption of fluid flow, there has been a continuing need for improvements which will overcome the problems inherent in prior art equipment. For example, various electrical timing devices are known for use in conjunction with pressure fluid circuits; however, there are several important applications of pneumatic systems wherein a source of electrical energy is not available or considered sufficiently reliable. There are also several types of pneumatic or other pressure fluid timing circuits which are also lacking in reliability due to the need to provide very clean air in a protected environment to the system itself, and/or to maintain a constant control pressure in the system to provide an accurate repeat cycle timing function. Here again, applications of many pneumatic systems which include devices utilizing small flow control orifices suffer from contamination problems and/or are susceptible to wide variation in working fluid and control fluid pressures.
Two important applications of pneumatic timing devices lack substantially all of the requisites indicated above for trouble free operation of prior art timing apparatus. For example, in the application of dust collection and filtration units used in conjunction with blasthole drilling equipment and other industrial applications, it is known to use impingement or barrier type filter elements which are cleaned periodically by providing a momentary reverse flow of air through the filter elements to remove dust which was accumulated and caked on the upstream side of the filter media. The harsh environment in which many dust collection and filter units operate, and the unavailability of suitable electrical power, has made it particularly difficult to provide a suitable timing control system for effecting the reverse flow of pressure air for periodically cleaning the filter elements. Moreover, in most applications of this type of equipment it is highly desirable to maintain mechanical simplicity and reliability of the equipment and associated control devices, and to utilize control air from the same source as the working fluid, such as, in the case of drilling rigs, the on board compressor which is supplying bailing air for the drilling function. Furthermore, the wide variation in air supply pressures available on different types of drilling equipment as well as in other industrial compressed air systems is particularly bothersome in terms of developing a suitable repeat cycle timing system.
Another demanding application of a repeat cycle pneumatic timing device is in connection with equipment for maintaining suitable flow from bulk material storage bins and the like. For example, there is a technique to prevent clogging and flow interruption in large bulk material storage bins wherein a nozzle is properly arranged in the flow path of material in the bin to provide a momentary blast of air to loosen compacted material in the bin dischage portion. Here again, it is desirable to provide a timing control system which provides a constant cyclic pulse of fluidizing or blasting air, which is not susceptible to the harsh environment including contamination of the compressed air circuit and which is not affected by variations in pneumatic system supply pressure.
All of the desired features associated with providing the timing control function for the abovenoted types of equipment are provided by the present invention, which invention may be used in other applications as will be appreciated by those skilled in the art.